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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.overview.ssl"></a><a class="link" href="ssl.html" title="SSL">SSL</a>
</h3></div></div></div>
<p>
        Boost.Asio contains classes and class templates for basic SSL support. These
        classes allow encrypted communication to be layered on top of an existing
        stream, such as a TCP socket.
      </p>
<p>
        Before creating an encrypted stream, an application must construct an SSL
        context object. This object is used to set SSL options such as verification
        mode, certificate files, and so on. As an illustration, client-side initialisation
        may look something like:
      </p>
<pre class="programlisting"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">sslv23</span><span class="special">);</span>
<span class="identifier">ctx</span><span class="special">.</span><span class="identifier">set_verify_mode</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">verify_peer</span><span class="special">);</span>
<span class="identifier">ctx</span><span class="special">.</span><span class="identifier">load_verify_file</span><span class="special">(</span><span class="string">"ca.pem"</span><span class="special">);</span>
</pre>
<p>
        To use SSL with a TCP socket, one may write:
      </p>
<pre class="programlisting"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;</span> <span class="identifier">ssl_sock</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">,</span> <span class="identifier">ctx</span><span class="special">);</span>
</pre>
<p>
        To perform socket-specific operations, such as establishing an outbound connection
        or accepting an incoming one, the underlying socket must first be obtained
        using the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span></code> template's <a class="link" href="../reference/ssl__stream/lowest_layer.html" title="ssl::stream::lowest_layer"><code class="computeroutput"><span class="identifier">lowest_layer</span><span class="special">()</span></code></a>
        member function:
      </p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">::</span><span class="identifier">lowest_layer_type</span><span class="special">&amp;</span> <span class="identifier">sock</span> <span class="special">=</span> <span class="identifier">ssl_sock</span><span class="special">.</span><span class="identifier">lowest_layer</span><span class="special">();</span>
<span class="identifier">sock</span><span class="special">.</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">my_endpoint</span><span class="special">);</span>
</pre>
<p>
        In some use cases the underlying stream object will need to have a longer
        lifetime than the SSL stream, in which case the template parameter should
        be a reference to the stream type:
      </p>
<pre class="programlisting"><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span> <span class="identifier">sock</span><span class="special">(</span><span class="identifier">my_io_context</span><span class="special">);</span>
<span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&amp;&gt;</span> <span class="identifier">ssl_sock</span><span class="special">(</span><span class="identifier">sock</span><span class="special">,</span> <span class="identifier">ctx</span><span class="special">);</span>
</pre>
<p>
        SSL handshaking must be performed prior to transmitting or receiving data
        over an encrypted connection. This is accomplished using the <code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span></code>
        template's <a class="link" href="../reference/ssl__stream/handshake.html" title="ssl::stream::handshake">handshake()</a>
        or <a class="link" href="../reference/ssl__stream/async_handshake.html" title="ssl::stream::async_handshake">async_handshake()</a>
        member functions.
      </p>
<p>
        Once connected, SSL stream objects are used as synchronous or asynchronous
        read and write streams. This means the objects can be used with any of the
        <a class="link" href="../reference/read.html" title="read">read()</a>, <a class="link" href="../reference/async_read.html" title="async_read">async_read()</a>,
        <a class="link" href="../reference/write.html" title="write">write()</a>, <a class="link" href="../reference/async_write.html" title="async_write">async_write()</a>,
        <a class="link" href="../reference/read_until.html" title="read_until">read_until()</a> or <a class="link" href="../reference/async_read_until.html" title="async_read_until">async_read_until()</a>
        free functions.
      </p>
<h5>
<a name="boost_asio.overview.ssl.h0"></a>
        <span class="phrase"><a name="boost_asio.overview.ssl.certificate_verification"></a></span><a class="link" href="ssl.html#boost_asio.overview.ssl.certificate_verification">Certificate
        Verification</a>
      </h5>
<p>
        Boost.Asio provides various methods for configuring the way SSL certificates
        are verified:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            <a class="link" href="../reference/ssl__context/set_default_verify_paths.html" title="ssl::context::set_default_verify_paths">ssl::context::set_default_verify_paths()</a>
          </li>
<li class="listitem">
            <a class="link" href="../reference/ssl__context/set_verify_mode.html" title="ssl::context::set_verify_mode">ssl::context::set_verify_mode()</a>
          </li>
<li class="listitem">
            <a class="link" href="../reference/ssl__context/set_verify_callback.html" title="ssl::context::set_verify_callback">ssl::context::set_verify_callback()</a>
          </li>
<li class="listitem">
            <a class="link" href="../reference/ssl__context/load_verify_file.html" title="ssl::context::load_verify_file">ssl::context::load_verify_file()</a>
          </li>
<li class="listitem">
            <a class="link" href="../reference/ssl__stream/set_verify_mode.html" title="ssl::stream::set_verify_mode">ssl::stream::set_verify_mode()</a>
          </li>
<li class="listitem">
            <a class="link" href="../reference/ssl__stream/set_verify_callback.html" title="ssl::stream::set_verify_callback">ssl::stream::set_verify_callback()</a>
          </li>
</ul></div>
<p>
        To simplify use cases where certificates are verified according to the rules
        in RFC 6125 (identity verification in the context of Transport Layer Security),
        Boost.Asio provides a reusable verification callback as a function object:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
            <a class="link" href="../reference/ssl__host_name_verification.html" title="ssl::host_name_verification">ssl::host_name_verification</a>
          </li></ul></div>
<p>
        The following example shows verification of a remote host's certificate according
        to the rules used by HTTPS:
      </p>
<pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">;</span>
<span class="keyword">namespace</span> <span class="identifier">ssl</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">ssl</span><span class="special">;</span>
<span class="keyword">typedef</span> <span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">&lt;</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">socket</span><span class="special">&gt;</span> <span class="identifier">ssl_socket</span><span class="special">;</span>

<span class="comment">// Create a context that uses the default paths for</span>
<span class="comment">// finding CA certificates.</span>
<span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span> <span class="identifier">ctx</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">sslv23</span><span class="special">);</span>
<span class="identifier">ctx</span><span class="special">.</span><span class="identifier">set_default_verify_paths</span><span class="special">();</span>

<span class="comment">// Open a socket and connect it to the remote host.</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">io_context</span><span class="special">;</span>
<span class="identifier">ssl_socket</span> <span class="identifier">sock</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">,</span> <span class="identifier">ctx</span><span class="special">);</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span> <span class="identifier">resolver</span><span class="special">(</span><span class="identifier">io_context</span><span class="special">);</span>
<span class="identifier">tcp</span><span class="special">::</span><span class="identifier">resolver</span><span class="special">::</span><span class="identifier">query</span> <span class="identifier">query</span><span class="special">(</span><span class="string">"host.name"</span><span class="special">,</span> <span class="string">"https"</span><span class="special">);</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">connect</span><span class="special">(</span><span class="identifier">sock</span><span class="special">.</span><span class="identifier">lowest_layer</span><span class="special">(),</span> <span class="identifier">resolver</span><span class="special">.</span><span class="identifier">resolve</span><span class="special">(</span><span class="identifier">query</span><span class="special">));</span>
<span class="identifier">sock</span><span class="special">.</span><span class="identifier">lowest_layer</span><span class="special">().</span><span class="identifier">set_option</span><span class="special">(</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">no_delay</span><span class="special">(</span><span class="keyword">true</span><span class="special">));</span>

<span class="comment">// Perform SSL handshake and verify the remote host's</span>
<span class="comment">// certificate.</span>
<span class="identifier">sock</span><span class="special">.</span><span class="identifier">set_verify_mode</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">verify_peer</span><span class="special">);</span>
<span class="identifier">sock</span><span class="special">.</span><span class="identifier">set_verify_callback</span><span class="special">(</span><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">host_name_verification</span><span class="special">(</span><span class="string">"host.name"</span><span class="special">));</span>
<span class="identifier">sock</span><span class="special">.</span><span class="identifier">handshake</span><span class="special">(</span><span class="identifier">ssl_socket</span><span class="special">::</span><span class="identifier">client</span><span class="special">);</span>

<span class="comment">// ... read and write as normal ...</span>
</pre>
<h5>
<a name="boost_asio.overview.ssl.h1"></a>
        <span class="phrase"><a name="boost_asio.overview.ssl.ssl_and_threads"></a></span><a class="link" href="ssl.html#boost_asio.overview.ssl.ssl_and_threads">SSL
        and Threads</a>
      </h5>
<p>
        SSL stream objects perform no locking of their own. Therefore, it is essential
        that all asynchronous SSL operations are performed in an implicit or explicit
        <a class="link" href="core/strands.html" title="Strands: Use Threads Without Explicit Locking">strand</a>. Note that
        this means that no synchronisation is required (and so no locking overhead
        is incurred) in single threaded programs.
      </p>
<h5>
<a name="boost_asio.overview.ssl.h2"></a>
        <span class="phrase"><a name="boost_asio.overview.ssl.see_also"></a></span><a class="link" href="ssl.html#boost_asio.overview.ssl.see_also">See
        Also</a>
      </h5>
<p>
        <a class="link" href="../reference/ssl__context.html" title="ssl::context">ssl::context</a>, <a class="link" href="../reference/ssl__host_name_verification.html" title="ssl::host_name_verification">ssl::host_name_verification</a>,
        <a class="link" href="../reference/ssl__stream.html" title="ssl::stream">ssl::stream</a>, <a class="link" href="../examples/cpp11_examples.html#boost_asio.examples.cpp11_examples.ssl">SSL example (C++11)</a>.
      </p>
<h5>
<a name="boost_asio.overview.ssl.h3"></a>
        <span class="phrase"><a name="boost_asio.overview.ssl.notes"></a></span><a class="link" href="ssl.html#boost_asio.overview.ssl.notes">Notes</a>
      </h5>
<p>
        <a href="http://www.openssl.org" target="_top">OpenSSL</a> is required to make use
        of Boost.Asio's SSL support. When an application needs to use OpenSSL functionality
        that is not wrapped by Boost.Asio, the underlying OpenSSL types may be obtained
        by calling <a class="link" href="../reference/ssl__context/native_handle.html" title="ssl::context::native_handle"><code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">context</span><span class="special">::</span><span class="identifier">native_handle</span><span class="special">()</span></code></a> or <a class="link" href="../reference/ssl__stream/native_handle.html" title="ssl::stream::native_handle"><code class="computeroutput"><span class="identifier">ssl</span><span class="special">::</span><span class="identifier">stream</span><span class="special">::</span><span class="identifier">native_handle</span><span class="special">()</span></code></a>.
      </p>
</div>
<div class="copyright-footer">Copyright © 2003-2024 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div>
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